Whether the latest stab at 3-D emerges as the single most revolutionary change for movies since color, as DreamWorks CEO Jeffrey Katzenberg has predicted, or becomes the Smell-O-Vision of the new millennium remains to be seen. But fueled by better technologies, a growing number of 3-D-equipped theaters, and some heady financial reasons for moving forward, 3-D is once again back -- and this time, to stay.

While there are 3-D-ready TVs for sale -- primarily, rear-projection DLP sets from Mitsubishi and Samsung (the latter also offers a plasma model) -- the real 3-D resurgence is in theaters, where the trickle that began with The Polar Express 3-D in 2004 and Chicken Little 3-D in '05 has swelled to a steady stream. In just the past 2 years alone we've seen Monster House, The Ant Bully, Beowulf, Meet the Robinsons, Shark Boy and Lava Girl, U2 3-D, Hannah Montana and Miley Cyrus: Best of Both Worlds Concert, Fly Me to the Moon, The Nightmare Before Christmas, Journey to the Center of the Earth, and Bolt dazzle bespectacled audiences.

But 2009 is when the 3-D flirtation will turn into a full-blown affair. Most of the major studios are working on 3-D titles, and both Disney/Pixar and DreamWorks Animation have made 3-D a major part of their future strategies. Disney/Pixar plans to release eight animated 3-D features in the next few years, including the next Toy Story installment and a Cars sequel. DreamWorks Animation has said that all its pictures going forward -- including Monsters vs. Aliens and Shrek the Fourth -- will be in 3-D.

Some of Hollywood's biggest directors are also joining the party. Upcoming 3-D releases include a trilogy based on The Adventures of Tintin from Peter Jackson and Steven Spielberg, a remake of A Christmas Carol by director Robert Zemeckis (who's now working exclusively in 3-D), and 3-D conversions of all six Star Wars movies (although it remains to be seen whether a 3-D Jar Jar Binks is a step forward or backward for the technology).

But maybe the most anticipated 3-D film of 2009 is James Cameron's sci-fi epic for 20th Century Fox, Avatar, said to be one of the most complex movies ever made. Slated for release in December, the film combines live action with an intricate CGI landscape and photorealistic digital actors. Before that, the studio will release Ice Age 3: Dawn of the Dinosaurs, a likely 3-D blockbuster.

Twice as Hard

If 3-D is so great, why didn't it catch on when it first hit the scene in the 1950s? For one, 3-D films are hard and expensive to make, adding about 10% to 20% to the cost of a movie. There are also technical challenges, particularly with live-action movies, since a pair of cameras must be synchronized to achieve the proper effect. That's why many current 3-D releases are animated films: Digital animation is essentially created in 3-D and just requires more computer crunch time to render the required second perspective.

All 3-D films require double images -- one for the right eye and a slightly different one for the left. When the images are correctly synchronized and viewed through special glasses, they converge, and your brain works its magic to produce the illusion of depth. Older 3-D films generated the images using two hard-to-sync projectors, each of which created a layer of color. The audience viewed the movie using cheap cardboard glasses -- anaglyphic models, with one blue and one red plastic lens -- that separated the two images. Because it was hard to coordinate the two projectors, viewing could cause eyestrain, headaches, and even nausea.

Although the principle is the same, newer digital 3-D schemes use different technologies to improve performance and comfort. Most notably, 3-D images can be generated with just one projector, which flashes alternating sequential images for each eye. While all digital 3-D movies are shot at 48 frames per second, that rate is "triple flashed" inside the theater to 144 fps (each frame is presented three times) so viewers don't see the sequential flashing.

Several companies are vying for the growing 3-D market. The leader is Real D, whose DLP-based technology is employed in more than 90% of U.S. theaters that show 3-D. Real D uses circular polarization, where an electronic filter called a Z-screen encodes light with different polarities for the left and right images. Viewers wear polarized glasses, so each eye receives the correct polarized image. Theaters need to be outfitted with highly reflective silver screens that can maintain the polarization of the images, but the glasses are inexpensive disposable models with round lenses. Real D has started replacing Z-screen filters with a new technology that can recapture some of the light lost during polarization, for improved brightness (and, therefore, larger screen sizes).

Another competitor is Dolby, which uses a technology called spectral division. Here, a spinning filter wheel splits the primary colors into separate frequencies for each eye. Viewers wear spectral-division glasses with coatings that filter out the unwanted images for each eye. While conventional theater screens are used, the glasses must be returned and washed before each use.

XpanD, which uses active LCD shutter glasses that sync to the projector's flash by way of RF signals, has signed a deal to outfit a small U.S. theater chain this summer. Meanwhile, George Lucas is using technology from a company called In-Three to convert the Star Wars films to 3-D. And longtime 3-D player Imax, with its super-size screens, is in the midst of a film-to-digital conversion.